Sexual transmission through mucosal surfaces has been the most common route of HIV-1 spread throughout the world. Although much attention has been focused on vaccine development for HIV-1, progress has been slow and there is an urgent need to find alternative approaches, such as topical microbicides, to target the spread of HIV-1. Human a- and -defensins contribute to innate immune defenses against microbial and viral infections; however, these endogenous factors are minimally effective in preventing the spread of HIV. Certain nonhuman primates also produce ?-defensins - 18 residue cyclic peptides that act as HIV-1 entry inhibitors. Multiple human ?-defensin genes exist, but they harbor a premature termination codon that blocks translation. Consequently, the ?-defensins encoded within the human genome (called retrocyclins in humans) are not expressed as peptides. Based on the genetic code contained within the otherwise intact retrocyclin genes, we recreated retrocyclins synthetically, and revealed them to be remarkably active against R5 and X4 isolates from a wide variety of HIV-1 clades. While in vivo production of ?-defensins in rhesus macaques involves the post-translational ligation of two nine-residue peptides, neither the mechanism of this unique process nor its existence in human cells was known - until now. We are proposing a paradigm shift in how a microbicide could act to prevent HIV-1 transmission, through the use of inexpensive and widely available aminoglycoside antibiotics to enhance vaginal innate immunity against HIV-1. In eukaryotes, aminoglycosides can suppress premature termination codons through the incorporation of an amino acid in its place. In preliminary studies, we restored the expression of retrocyclin peptides by human promyelocytic and HeLa cells using aminoglycosides that suppressed retrocyclin's premature termination codon, and revealed that these natural retrocyclins were active against HIV-1. Based on our studies, we hypothesize that aminoglycosides can restore the natural production of retrocyclins in the cervicovaginal mucosa, and can be formulated as quick-release films to confer increased protection against sexually transmitted HIV-1. With assistance from a multidisciplinary team, we will test these hypotheses in the R21 phase by: 1) assessing the ability of aminoglycosides to induce sustained expression of retrocyclins in human vaginal epithelial cells, organotypic cervicovaginal tissues and cervical organ cultures, and 2) evaluating the ability of topically applied aminoglycosides to induce in vitro and ex vivo toxicity and proinflammatory cytokines in the vaginal mucosa. A lead aminoglycoside, exhibiting the greatest activity while exhibiting minimal adverse effects to the vaginal mucosa, will proceed to the R33 phase in which we will: 3) formulate the aminoglycoside as a quick-release film to induce natural anti-HIV-1 retrocyclin expression, and 4) evaluate the vaginal safety of the film-formulated aminoglycoside in pigtailed macaques. Aminoglycoside-mediated translation of retrocyclins could result in a new class of microbicide to prevent HIV-1 transmission.